Grease-resisting box board



. suitable Patented Jan. 3, 19 33 .uNiTEo STATES PATENT oFrlcE CARLETON ELLIS, OF MONTGLAIR NEW JERSEY, ASSIGNOR T ELLIS-FOSTER COH- PANY, A CORPORATION OF NEW JERSEY GREASE-BESISTING BOX BOARD No Drawing.

This invention relates to grease-proof paper or paper which is relatively resistant to penetration by greasy substances and to the process of making same, and the inven tion also includes as an article of manufacture containers made from such grease-resisting paper: y

In using the term paper herein, I embrace not only the thinner grades of paper, but also the heavier grades, particularly those designated as board stock.

The present invention enables thin greaseresisting paper to be made which in itself is not sufiiciently thick or rigid to be self-supporting, but may be employed as a lining for containers made of stiffer material. On the other hand by treating paper board in the manner described herein, I am enabledto secure a sheet which has suflicient strength and rigidity to be employed of itself in making boxes, cartons, ice cream containers, milk and other liquid containers, oyster pails and the those containing ground wood. Thus I'am able to employ a mixture of ground wood and sulphite pulp and the like to make a board limit myself toany particular grade or thickness of paper and paper board.

The paper may suitably sized if desired with rosin'size or with wax emulsion, or with mixtures of rosin-size and wax emulsion, or the paper, durin formation, may be built up of layers of p p with intermediate layers of asphalt or other waterproofing emulsion and thelike'..

Preferabl I employ a paper or board made from groun wood and sulphite pulp or simior the purpose. I do not, however,

Application filed August 22,1927. Serial Ho. 214,781.

has been added in the form of an emulsion in the beater.

' In whichever way prepared the dry paper is coated preferably only on one side with a grease-resisting composition comprising a compound of cellulose which is soluble in organic solvents, including nitrocellulose, cellulose acetate, and cellulose ethers.

The present invention will be described particularly with reference to the employment of nitrocellulose. While high viscosity nitrocellulose such as smokeless powder, or celluloid cotton may be used in the composition employed, I prefer to utilize nitrocellulose of low viscosity. Thus on the one hand I may employ the extremely low viscosity nitrocellulose ranging from one second, down to one-half second or even lower, or I may use intermediate low viscosity ranging from 1 or 2 seconds up to 4 or 5 seconds, or still higher viscosities running from 5 to seconds.

Smokeless powder which has become too old to be employed in military operations afi'ords a cheap supply of nitrocellulose. It is, however, of such high viscosity that a large amount of solvent would be required to form a solution which could be readily applied to the paper to produce the greaseresisting coating. Preferably, therefore, I employ smokeless powder of reduced viscosity. This may be obtained by heating the smokeless powder or by treating it in solution with ammonia or other alkali agents as is now known in the art.

Thus smokeless powder may be dissolved in acetone and a small amount of ammonia gas allowed to pass into the solution. On standing for a few hours reduction in viscosity will take place, and any free ammonia may be suitably neutralized. Treatment with chemical agents in this manner tends somewhat to discolor the nitrocellulose in some cases, unfitting the solution for use as a lacquer for certain purposes, but in the present invention the paper itself in its preferred form, that is one containing ground wood or its equivalent or other low grade paper raw material, does not yield a paper or board which is white in color, but one 50 lar fibrous material, containing. wax which which is yellowish or brownish. 1

As solvents for the nitrocellulose, I have preferred to employv highly volatile ones.

The more expensive high boiling solvents, such as amyl acetate, butyl acetate, ethyl lactate and the like are costly, and while I propose to recover the solvents as far as possible,

- there is alwayssome loss, and the solvent cost is thus considerably increased when more expensive solvents are used.

A solvent such as acetone has many advantages, one being that it forms probably the least viscous nitrocellulose solution of any to avoid since the weakeningof the coatingdue to blushing, renders the coating more liable to crack on folding when the coated paper is formed into a box or carton- It is desirable to avoid any cracking at the creases.

In Serial No. 117,152, filed June 19, 1926, I have disclosed the use of a blush-corrective resin employed in a coating composition compatibility for nitrocellulose.

comprising nitrocellulose dissolved in a volatile vehicle of a blush-forming character, and with respect to certain phases of the present invention certain features disclosed in the aforesaid application are employed herein with reference to the grease-proofing of paper.

Unlike natural resins which have no such action on nitrocellulose and which merely mix with nitrocellulose in solution, certain types of synthetic resins have been found to possess a noticeable colloidingeffect and great Particularly is this true of those synthetic resins which can be made by chemically combining glycerol or other polyhydric alcohols with phthalic acid or its anhydride. or various modifications thereof. Other polybasic acids such as citric, tartaric, maleic, malic, and like substances, are,in most cases, suitable for similar purposes. In place of glycerol, I may employ such other polyhydric alcohols as ethylene and propylene lycols, mann-itol, pentaerythritol,and.like su stances. Various mlxtures of acids are often more desirable than any one acid. Thus resins made from phthalic anhydride and glycerol may be advantageously modified by incorporating certain amounts of the fatty acids of various 0115 such as cottonseed oil, linseed'oil, and the like, or by means of monobasic carboxylic acids, such as benzoic, salicylic, benzoyl-benzoic acid, and the like.

One suitable resin, for example, is made substantially as follows:

47 parts by weight of glycerol are added to'80 parts by weight of phthalic anhydride and 49 parts by weight of the distilledlfatty than twenty. Another suitable resin is made from glycerol 47 partsby weight, phthalic anhydride 118 parts by weight, and benzoic acid 98 parts by weight. This resin is made in identical manner as the foregoing resin.

Still another suitable resin of a harder nature may be made by combining l7 parts by weight of glycerol with 9 parts by weight of phthalic anhydride. This mixture is inclined to polymerize and become infusible at higher temperatures, or if heated for too long a period, so that it is advisable to heat this mixture to a temperature not substantially in excess of 230 0., and continuing until a sample has shown the'desired degree of hardness.

These synthetic resins are soluble in acetone and many other solvents and may be in corporated with nitrocellulose in any desired proportion to form suitable coatings. It is usually necessary to employ a' fairly large proportion of these resins, for example, at least equal parts of resins and nitrocellulose and preferably somewhat more, in order to obtain the desired effect. Plasticizers or I softeners for nitrocellulose may be added where desired, such materials as diethyl or dibutyl phthalate and tricresyl phosphate being especially recommended.

These synthetic resins with nitrocellulose, with or without plasticizers, pigments, dyes, or other substances, may be dissolved in acetone, ethyl acetate, mixtures thereof, with or without the addition of diluents such as .low boiling alcohols, benzol, and the like, to

from natural resins such as rosin, rosin ester and damar, or other resins which have no appreciable solvent action for the nitrocelluose.

One suitable composition may be made by dissolving one part by weight of one-half second viscosity nitrocellulose and'2 parts by weight of a cottonseed fatty acid phthalic glyceride resins in 7 parts by weight of acetone. Other synthetic resins having for nitrocellulose the properties aforesaid, may be emplov ed in place of the one specified.

Esteri ed rosin such as rosin glyceride, or ordinary ester gum may be added to the above compositions, also the glycol esters of rosins, or the glycol-ether esters of rosin. Likewise other resins and balsams may be introduced where such addition cheapcns the composition without destroying its desirable properties. I

The following will illustrate different compositions suitable for the coating operation:

Example I Low viscosity nitrocellulose one part by weight was dissolved in acetone 4 parts, forming a 20% solution.

Cottonseed phthalic glyceride resin was dissolved in an equal volume of acetone, thus making a 50% solution.

A. paper coating composition was made by mixing 8 partsby weight of the resin solution, with 20 parts of the nitrocellulose solution, adding one part of dibutyl phthalate.

The viscosity of this solution is quite low, and it may be applied to paper by brushing or coating apparatus. It may be made of even higher consistency when applied with special coating means.

Example I I Low viscosity nitrocellulose was dissolved in a mixture of equal volumes ethyl acetate and benzol to form a 20% solution.

Cottonseed phthalic glyceride resin was dissolved in a similar composite solvent to make a 50% solution.

These were mixed in the same proportions as stated in Example I, including the fiddle tion ofone part of dibutyl phthalate. The viscosity was considerably higher than that of Example 1, although the same grade of nitrocellulose was used in both cases. In order to obtain approximately the viscosity of Example I, the composition of Example II was diluted with 7 parts of a mixture of equal parts ethyl acetate and benzol.

This was applied to paper and paper board and gave an excellent coating.

E mampl e I l I An alcohol-soluble nitrocellulose of second viscosity, one part, was dissolved in a mixture of denatured alcohol, 2 parts; ethyl acetate, one part; benzol, 2 parts.

Cottonseed phthalic glyceride resin was dissolved in an equal weight of a mixture of .equal parts denatured alcohol and benzol.

natured alcohol and benzol were added. This composition was applied successfully to paper to form a grease-resisting coating.

The process of applying these solutions to the paper surface preferably consists in passing the web of paper through coating rolls to which the composition is fed, and immediately passing the coated paper into a drying oven, where at a gentle heat the highly volatile solvents evaporate quickly and are withdrawn by a pump to a solvent recovery apparatus. Since the paper preferably is coated only on one side, it is very readily handled in the coating apparatus, and on the carriers conveying to the drying chamber.-

The final operation forming a feature of the preferred embodiment is that" of hot calendering the coated surface. The grease resisting qualities appear to be increased by hot calendering, and various slight blemishes,

particularly irridescent spots or areas, are

eliminated. The temperature of the calender rolls will vary depending on the composition employed for coating and the speed of travel of the web of paper through the rolls. Preferably, I allow just enough heat and time of contact to slightly soften the coated surface. By employing a synthetic resin or balsam having amild solvent effect on the nitrocellulose at elevated temperatures, an improved grease-resisting effect results.

It should be noted that the coating thus applied does not need to be thick, but may be of such thinness that the finished paper or board shows scarcely any evidence of treatment, such very thin nearly invisible coatings after hot calendering serving to provide a sufficient grease-resistance, so that the resulting board may be made into cartons for crackers and other foods containing a considerable amount of shortening and not showing grease marks through the board, even though the crackers or biscuit may be in contact therewith for a long period of time.

The board thus may be treated with the grease-repellent resinated nitrocellulose to form a surface impregnum which scarcely increases the thickness of the paper. This thin surfacing of resinated nitrocellulose applied only to one side of the board enables paper to be folded into box shape with the surfacing, or surface impregnum, on the interior of the box only. The folding of the paper or board therefore does not stretch the surfacing, but contracts or compresses it, as the folding is, in most cases, inward on the side where the surfacing exists. Thereby a carton adapted as a package for fat-shortened food products, such as biscuit, crackers, and cookies is obtained, comprising paper folded in box shape carrying,interiorly only, a grease-resisting surface impregnum containing nitrocellulose and a grease-resisting resin.

It may be noted that I have employed a cottonseed phthalic glyceride resin in the 'a foreign odor. Similarly fatty acids of other vegetable oils such as peanut oil, corn oil, soya bean oil, etc., may be incorporated in resinous combination as described above. Castor oil may be used in some cases. The vegetable glycerides themselves may be resinified with phthalic anhydride or similar organic acid and gylcol ethers. A striking feature of the glyceride and glycol resins and the like from the standpoint of the present invention is their repellant action on fatty oils. For: example, the, cottonseed phthalic glyceride, although containing in combination the fatty acid components of cottonseed oil, is surprisingly resistant to animal and vegetable oils used in shortening, and this property enables the resin to serve to fortify and enhance any grease-proofing qualities which nitrocellulose may possess.

The preferred coating or surfacing therefore consists of or contains nitrocellulose preferably of reduced viscosity, and a greaserepellent resin or balsam. The grease-repellant resins and balsams of the synthetic type may as aforesaid comprise a very large group of differing chemical and physi-- cal properties, but having in common the grease-repellant characteristic. This group includes resins made from crystalline organic acids and their anhydrides, with such chemically different substances as glycols, chlorhydrines, glycol ethers, and glycerol, polyglyc- 'erol, and organic oxide such as ethylene or butylene oxide.

Other solvent mixtures which may be used in the foregoing examples, or in modified.

combustibility of the nitrocellulose coating,

tricresyl phosphate or triphenyl phosphate may be used for the purpose. It should be noted, however, that the presence of the resin in the resinated nitrocellulose considerably reduces the rapidity of combustion of the latter, depending upon the proportion of resin present. Cellulose acetate may be used to partly or wholly replace thenitrocellulose in cases where nitrocellulose is not desired.

As indicated above the ratio between nitrocellulose and resin may be varied considerably. This will depend to some extent upon the character of the paper,' on the flexibility or pliability desired in the surfacing, on the length of time that the surface paper is likely 'to be kept before being cut and folded into cartons, as well as on other'factors. A high roportion of nitrocellulose, that is, a major proportion, may be used in some cases, while in other cases the resin may predominate until ultimately a composition is reached .where a small proportion of nitrocellulose merely serves to toughen a large proportion of resin. The extremes on-the one hand are represented by nitrocellulose alone, and on the other hand by the resin alone, and compositions made up with either of these extremes may be employed in some cases for special purposes.

With respect to the additions of natural resins and the like. referred'to above, a large proportion may easily impair the greaserepellent qualities of the synthetic resin, and any such dilution or cheanening of the resin by such additions should be avoided, since for best results i prefer not to use any resin soluble in the common fatty oils employed as shortening.

Preferably dye or coloring matter is not used in the resinated n trocellulose solution, but the use of such coloring agents is not precluded, and ii the exterior of the carton is to be coated or surfaced with the resinated nitrocellulose sometimes it is desirable to employ a dye-stud in the coating composition.

While the surfac ng of resinated nitrocellulose increaseswater-resistance, I prefer to employ, as l have indicated above, a board which has been made from paper pulp. to

which a wax size, with or without a rosin size, has been incorporated prior to forming the pulp into sheets. By usingsuch wax-containing paper and supplement ng the effect of the wax by the resinated nitrocellulose surfacing, I am able to obtain excellent water and grease resistance. This effect is improved by hot calendering.

When the board is used to make cartons it 7 is desirable in some cases to pass it through hot rolls just before folding in order to render the coating more pliant. This is recommended particularly incold weather.

In order to prevent diffusion of the vapors of the volatile solvents into the coating room,

' I may employ a small percentage of wax, such as parafiin or ceresine, in mixed solvents such as benzol-ethyl acetate. In my co-pencling applications on the production of floor coverings by applying a surfacing containing nitrocellulose and resin, to a paper backing, (e. gsaturated felt) I have disclosed the employment of wax in amounts less than 1%. In the present invention I find it possible to somewhat increase the proportion of wax as blemishes which may be caused by thewax are largely removed onvhot calendering. In any event, however, I'prefer not to use more than 2 or 3% of wax, based on the weight of the solvent mixture used.

In using the term resinated nitrocellulose I do not, of course, mean to imply that the nitrocellulose itself is resinated, but that it is incorporated with a resin, particularly one compatible therewith. v

In case the synthetic resins of the cottonseed phthalic glyceride type are too soft, and it is desired to use only a low percentage of nitrocellulose, these resins may be increased in melting point by heating with one or two per cent ormore of calcium hydrate, zinc hydrate or" other hydrates, or oxides, or of a number of the metals. The resins of this type also may be rendered somewhat harder by treatment with sulphur chloride and careful removal. of hydrochloric acid.

Referring again to the problem of-producing an odorless surfacing, or one which does not emit any odor of a disagreeable character, or dissimilar to that of the foods contained in the carton, interiorly surfaced with the composition of the present invention, I

' wish to call attention to the fact that the employment of castor oil in the free state, blown castor oil, blown rapeseed oil, and the like, commonly used as softeners and plasticizers in nitrocellulose lacquers, is dangerous in the present case because the tendency of such oils to grow rancid and emit a disagreeable odor makes the employment of more suitable plasticizing agents desirable. The synthetic resins disclosed in the present invention, in which a fatty oil or fatty acid is in combination, preferably should be so made that the acid number is very low. The reaction in making the resin should be carried far enough to avoid high acid numbers. I prefer to employ resins with acid numbers below 20, -or '30. Likewise in the case of nitrocellulose, I preferably avoid celluloid containing camphor because the latter gives a pronounced odor to food products. Furthermore, heavy solvents oftentimes employed as water eliminants in lacquers, leave a coating relativel slowly and may therefore generate an or in the carton. By avoiding such heavy solvents, using highly volatile solvents instead, and employing a surfacing which substantially does not increase the thickness of the paper in order to permit of thorough evaporation of the solvent in the short space of time permissible for evaporation, the con- 2. Wax-sized paper carrying nitrocellulose and polybasic aci -polyhydric alcohol syn thetic resin, the materials beingpresent in an amount to give substantial grease repellant properties to the paper.

3. Rosin-sized paper carrying nitrocellu lose and polybasic acid-pol hydric alcohol synthetic resin, the materials being present in an amount to give substantial grease repellant properties to the paper.

4:. Wrapping paper carrying a coating composition consisting essentially of nitrocellulose and polybasic acid-polyhydric alcohol synthetic resin, the materials being present in an amount to give substantial grease repellant properties to the paper and having been subjected to hot calendering subsequent to application.

5. A wrapping paper for grease containing articles, said paper carrying a coating of nitrocellulose and a polybasic acid-polyhydric alcohol synthetic resin, the materials being present in an amount to give substantial grease repellant properties to the paper.

6. A wrapping paper for grease containing articles, said paper carrying a coatin of nitrocellulose and a polybasic acid-pol hydric alcohol synthetic resin, thematerials being present in an amount to give substantial grease repellant properties to the paper, said paper having been subjected to hot calendering subsequent to the application of the coating.

7. A carton for containing greasy articles consisting of a paper coated with a material consisting essentially of nitrocellulose and polybasic acid-polyhydric alcohol synthetic resin, the materials being present in an amount sutficientto give substantial grease repellant properties to the paper.

8. A carton for containing greasy articles consisting of paper coated with a material consisting essentially of nitrocellulose and polybasic acid-polyhydric alcohol synthetic resin, the materials being present in an amount sufiicient to give substantial grease repellant properties to the paper, said coating 'compositionhaving been subjected to hot calendering subsequent to its application to the paper.

CARLETON ELLIS.

ditions are favored for production of a coating which does not generate an odor in the carton. If instead a heavy varnish-like s'urface were produced, a residual solvent may tend to create odors. What I claim is: 1. Paper carrying nitrocellulose and a polybasic acid-polyhydric alcohol synthetic resin,

the materials being present in an amount to give substantial grease repellant properties to the paper. 

